Bug 11304: fix display of detail page holdings tab in translated Bootstrap theme

Bug 11304: fix display of detail page holdings tab in translated Bootstrap theme

Detail page tabs are not displayed properly because JavaScript is broken
in French. This is due to _(' JS string construction used in place of
_(".

This patch fixes:

  - opac-detail.tt page
  - xt/single_quotes to test bootstrap theme

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Tested by applying the patch, running translate update, then translate
install. Saw no JavaScript error on the French detail page.

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Switches from single to double quotes for translatatable strings.
Unit tests for xt/single_quotes passes now.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>